Energy constraint has become an important factor in the design of MAC protocols. This paper addresses the issue of providing deterministic timing guarantees in the wireless LAN while minimizing energy consumption of the wireless nodes. We present a centralized energy efficient algorithm, Scheduled Contention Free Burst (S-CFB), which is built upon the recently proposed Hybrid Coordination Function (HCF) in the IEEE 802.11 standard. Two mechanisms are proposed: 1) bundling message transmissions into multiple contention free bursts in order to reduce control overhead; 2) allowing wireless nodes to sleep by avoiding preemption whenever possible. Our performance study shows that S-CFB meets the timing requirement for real-time messages, allows wireless nodes to switch to idle state for a longer period of time, and reduces the number of control frames required to maintain contention free transmission.